Student-professor team finds biological kink in fungal taxonomy

January 2011

A discovery reported in Ian Sheffer's ('07') undergraduate honors thesis, and later published in the scientific journal Mycotaxon could change the way scientists identify watermolds - any of about 150 species of fungi belonging to the order Saprolegniales.

A centuries-old taxonomic system classifies these organisms by sexual and asexual morphological traits, but wide and overlapping variation in the shape and arrangement of the reproductive structures historically has made identification difficult.

Identifying these water-dwelling organisms is crucial because watermolds are of profound ecological and economic importance worldwide. Although most are beneficial to the environment, a significant number are dangerous plant or animal pathogens.

David Padgett, a retired UNC Wilmington biologist and expert in mycology for more than 35 years, suspected that the identification criteria were flawed when, subsequent to collecting hundreds of watermolds from all over the world, he and his collaborator Dr. Craig Bailey found that 90% of them were not identifiable. Padgett, thus, designed a study to test the validity of the criteria. This test became the subject of Sheffer's undergraduate honor's thesis.

Using the reasoning that all 'clones' derived from a single, pure watermold colony should be identifiable to the same species as the original, Sheffer isolated ten subcultures from a single Saprolegniales parent colony. He subsequently analyzed each to determine whether four taxonomically important sexual characters differed statistically from the base culture or from each other. He found that eight of the eleven cultures differed significantly from at least one other culture with respect to two or more characters thus showing that clones derived from the same original colony could be identified as different species. Sheffer's experiment, therefore, called the validity of accepted identification criteria into serious question.

In order to determine whether or not the dramatic finding reported in Sheffer's honors thesis applied to a wide range of watermold species, Padgett used the same statistical test to analyze data derived from 45 collected specimens representing at least 3 watermold genera. Results of this broader experiment showed that 39 of the 45 were so variable that they could be identified as more than one species. This finding, also recently published in the scientific journal Mycotaxon, strongly supports Sheffer's finding as being applicable to a large number of watermolds.

Why watermold morphology is so variable remains unclear given the fact that it is genetically controlled. Padgett maintains, nonetheless, that the present findings strongly argue that new criteria for naming them need to be found.

"This is a major discovery that would not have come to light without Ian Sheffer's hard work," Padgett says. "His contribution to science should reflect well on UNCW and particularly its honors program."